This invention is generally concerned with methods of making anionic clays. Such clays are characterized by crystalline structures that consist of positively charged layers that are separated by interstitial anions and/or water molecules. The positively charged layers are often comprised of metal hydroxides of divalent metal cations (e.g., Mg2+, Ca2+, Zn2+, Mn2+, Co2+, Ni2+, Sr2+, Ba2+ and Cu+) and trivalent metal cations (e.g., Al3+, Mn3+, Fe3+, Co3+, Ni3+, Cr3+, Ga3+, B3+, La3+ and Gl3+). The interstitial anions are usually NO3xe2x80x94, OHxe2x80x94, Clxe2x80x94, Crxe2x80x94, Ixe2x80x94, CO32xe2x88x92, SO42xe2x88x92, SIO32xe2x88x92, HPO32xe2x88x92, MnO4xe2x80x94, HGaO32xe2x88x92, HVO42xe2x88x92, ClO4xe2x80x94, BO32xe2x88x92, monocarboxylates (e.g., acetate) and dicarboxylates (e.g., oxalate), alkyl sulphonates (e.g., lauryl sulphonate) and various combinations thereof.
Therefore, anionic clays are further subdivided according to the identity of the atoms that make up their crystalline structures. For example, anionic clays in the pyroaurite-sjogrenite-hydrotalcite group are based upon brucite-like layers (wherein magnesium cations are octahedrally surrounded by hydroxyl groups) which alternate with interstitial layers of water molecules and/or various anions (e.g., carbonate ions). When some of the magnesium in a brucite-like layer is isomorphously replaced by a higher charged cation, e.g., Al3+, then the resulting Mg2+xe2x80x94Al3+xe2x80x94OH layer gains in positive charge. Hence, an appropriate number of interstitial anions, such as those noted above, are needed to render the overall compound electrically neutral.
The literature also teaches that as the concentration of Al3+ increases in a Brucite-type lattice, a reduction of the lattice parameter known as xe2x80x9caxe2x80x9d, takes place. The lattice parameter known as xe2x80x9ccxe2x80x9d also is reduced. The reduction in lattice parameter, a, is due to the smaller, plus three charged, Al3+ ions substituting for the larger, plus two charged Mg2+ ions. This higher charge causes increased coulombic forces of attraction between the positive charged Brucite-type layer and the negative interlayer ionsxe2x80x94thus giving rise to a decrease in the size of the interlayer itself.
Natural minerals that exhibit such crystalline structures include, but by no means are limited to, pyroaurite, sjogrenite, hydrotalcite, stichtite, reevesite, eardleyite, mannaseite, barbertonite and hydrocalumite. The chemical formulas for some of the more common synthetic forms of anionic clays would include: [Mg6Fe2(OH)16]CO3. 4H2O, [Mg6Al2xe2x80x94(OH)16]CO3.4H2O, [Mg6Cr2(OH)16]CO3.4H2O, [Ni6xe2x80x94Fe2(OH)16]C3.4H2O, [Ni6Al2(OH)16]CO3.4H2O, [Fe4Fe2(OH)12]CO3.#H2O, [Ca2Al (OH)6](OH)0.75xe2x80x94(CO3)0.1252.5H2O6]OH.6H2O, [Ca2Alxe2x80x94(OH)6]OH.3H2O, [Ca2Al(OH)6]OH.2H2O, [Ca2Alxe2x80x94(OH)6]OH, [Ca2Al(OH)6]Cl2H2O, [Ca2Al(OH)6]0.5CO32.5H2O, [Ca2Al(OH)6]0.5SO4.3H2O, [Ca2xe2x80x94Fe(OH)6]0.5SO4.3H2O, [(Ni, Zn)6Al2(OH)16]CO3.4H2O, [Mg6(Ni, Fe)2(OH)16](OH)2.2H2O, [Mg6Al2(OH)16xe2x80x94](OH)2.4H2O, [(Mg3Zn3)al2(OH)16]CO3.4H2O, [Mg6Al2(OH)16]SO4.xH2O, [Mg6Al2(OH)16](NO3)2.xxe2x80x94H2O, [Zn6Al2(OH)16]CO3.xH2O, [Cu6Al2(OH)16xe2x88x92]CO3.xH2O, [Cu6Al2(OH)16]SO4.xH2O and [Mn6Al2xe2x88x92(OH)16]CO3.xH2O, wherein x has a value of from 1 to 6.
Those skilled in this art also will appreciate that anionic clays are often referred to as xe2x80x9cmixed metal hydroxides.xe2x80x9d This expression derives from the fact that, as noted above, positively charged metal hydroxide sheets of anionic clays may contain two metal cations in different oxidation states (e.g., Mg2+ and Al3+). Moreover, because the XRD patterns for so many anionic clays are similar to that of the mineral known as Hydrotalcite, Mg6Al2(OH)16(CO3).4H2O, anionic clays also are very commonly referred to as xe2x80x9chydrotalcite-like compounds.xe2x80x9d This term has been widely used throughout the literature for many years (see for example: Pausch, xe2x80x9cSynthesis of Disordered and Al-Rich Hydrotalcite-Like Compounds,xe2x80x9d Clay and Clay Minerals, Vol. 14, No. 5, 507-510 (1986). Such compounds also are often referred to as xe2x80x9canionic clays.xe2x80x9d Indeed, the expressions xe2x80x9canionic clay,xe2x80x9d xe2x80x9cmixed metal hydroxidesxe2x80x9d and xe2x80x9chydrotalcite-like compoundsxe2x80x9d are often found very closely linked together. For example, in: Reichle, xe2x80x9cSynthesis of Anionic Clay Minerals (Mixed Metal Hydroxides, Hydrotalcite),xe2x80x9d Solid State Ionics, 22, 135-141 (1986) (at Paragraph 1, page 135) the author states: xe2x80x9cThe anionic clays are also called mixed metal hydroxides since the positively charged metal hydroxide sheets must contain two metals in different oxidation states. Crystallographically they have diffraction patterns which are very similar or identical to that of hydrotalcite (Mg6Al2(OH)16(CO3).4H2O); hence they have also been referred to as hydrotalcites or hydrotalcite-like.xe2x80x9d (emphasis added). U.S. Pat. No. 5,399,329 (see col.1, lines 60-63) contains the statement: xe2x80x9cThe term xe2x80x98hydrotalcite-likexe2x80x99 is recognized in this art. It is defined and used in a manner consistent with usage herein in the comprehensive literature survey of the above-referenced Cavani et al. article.xe2x80x9d Hence, for the purposes of the present patent disclosure, applicant will (unless otherwise stated) use the term xe2x80x9chydrotalcite-likexe2x80x9d compound(s) with the understanding that this term should be taken to include anionic clays, hydrotalcite itself as well as any member of that class of materials generally known as xe2x80x9chydrotalcite-like compounds.xe2x80x9d Moreover, because of its frequent use herein, applicant will often abbreviate the term xe2x80x9chydrotalcite-likexe2x80x9d with
The methods by which HTL compounds have been made are found throughout the academic and the patent literature. For example, such methods have been reviewed by Reichle, xe2x80x9cSynthesis of Anionic Clay Minerals (Mixed Metal Hydroxides, Hydrotalcite),xe2x80x9d Solid States Ionics, 22 (1986), 135-141, and by Cavani et al., CATALYSIS TODAY, Vol. 11, No. 2, (1991). In the case of hydrotalcite-like compounds, the most commonly used production methods usually involve use of concentrated solutions of magnesium and aluminum which are often reacted with each other through use of strong reagents such as sodium hydroxide, and various acetates and carbonates. Such chemical reactions produce hydrotalcite or hydrotalcite-like compounds which are then filtered, washed, and dried. The resulting HTL compounds have been used in many waysxe2x80x94but their use as hydrocarbon cracking catalysts, sorbents, binder materials for catalysts and water softener agents is of particular relevance to this patent disclosure.
It also is well known that HTL compounds will decompose in a predictable manner upon heating and that, if the heating does not exceed certain hereinafter more fully discussed temperatures, the resulting decomposed materials can be rehydrated (and, optionally, resupplied with various anions, e.g., CO3=, that were driven off by the heating process) and thereby reproduce the original, or a very similar, HTL compound. The decomposition products of such heating are often referred to as xe2x80x9ccollapsed,xe2x80x9d or xe2x80x9cmetastable,xe2x80x9d hydrotalcite-like compounds. If, however, these collapsed or metastable materials are heated beyond certain temperatures (e.g., 900xc2x0 C.), then the resulting decomposition products of such hydrotalcite-like compounds can no longer be rehydrated and, hence, are no longer capable of forming the original hydrotalcite-like compound.
Such thermal decomposition of hydrotalcite-like compounds has been carefully studied and fully described in the academic and patent literature. For example, Miyata, xe2x80x9cPhysico-Chemical Properties of Synthetic Hydrotalcites in Relation to Composition,xe2x80x9d Clays and Clay Minerals, Vol. 28, No. 1, 50-56 (1980), describes the temperature relationships and chemical identity of the thermal decomposition products of hydrotalcite in the face of a rising temperature regime in the following terms:
xe2x80x9cIt is of interest to know the form in which the Al occurs after thermal decomposition of the hydrotalcite structure. A sample with x=0.287, hydrothermally treated at 200xc2x0 C. for 24 hr, was calcined at 300xc2x0-1000xc2x0 C. in air for 2 hr. After calcination at 300xc2x0 C., both hydrotalcite and MgO were detected by X-ray diffraction, but after calcination at 400xc2x0-800xc2x0 C. only MgO could be detected. At 900xc2x0 C. MgO, MgAl2O4, and a trace of xcex3-Al2O3 were detected.xe2x80x9d (emphasis added, for reasons to be explained in the ensuing portions of this patent disclosure)
Miyata then goes on to note that:
xe2x80x9cThe crystallite size was smaller than 50 xc3x85 when the sample was calcined below 800xc2x0 C. This value was much smaller than that for MgO obtained from pure Mg(OH)2. On calcination above 800xc2x0 C., the crystallite size rapidly increased. The changes of the crystallite size and lattice parameter a have the same tendency. Consequently, Al substituting in MgO acts to inhibit crystal growth. If Al-containing MgO is reacted with water, it should first form hydrotalcite. Hydrotalcite calcined at 400-800xc2x0 C. with x=0.287 was hydrated at 80xc2x0 C. for 24 hr, and the products were examined by X-ray powder diffraction. According to Table 7, hydrotalcite was the only hydrated product detected in samples calcined at 400-700xc2x0 C. The lattice parameter a is the same as that of the original sample. The samples calcined at 800xc2x0 C. also formed only hydrotalcite but their lattice parameters are larger than that of the original sample. According to FIG. 1, the molar ratio of this product is x=0.235. On the other hand, Al2O3 does not react with water under the above-mentioned conditions. Therefore, the results suggest that Al enters product MgO when hydrotalcite is calcined between 400 and 700xc2x0 C.xe2x80x9d (emphasis added)
U.S. Pat. No. 5,459,118 (xe2x80x9cthe ""118 patentxe2x80x9d) describes the character of the materials that result from progressively heating hydrotalcite-like compositions (HTlc""s) in a passage running from col. 4, line 67 to col. 5, line 14. It reads as follows:
xe2x80x9cThe natural products of calcination or activation in inert gas of a HTlc is believed to be a spinel. In the range between the temperature at which HTlc decomposition commences (between 572xc2x0 and 752xc2x0 F.) (i.e., between 300xc2x0 C. and 400xc2x0 C.) and that of spinel formation (1652xc2x0 F.) (i.e., at 900xc2x0 C.) , a series of metastable phases form, both crystalline and amorphous. Therefore, the surface area, pore volume, and structure depend on the temperature of calcination. Upon calcination, the crystal structure of DHT-4A is decomposed at about 660xc2x0 F. (i.e., 349xc2x0 C.) when water and carbon dioxide evolved from the structure, and a MgOxe2x80x94Al2O3 solid solution of formula 4.5 MgO.Al2O3 is formed. This solid solution is stable up to 1472xc2x0 F. (i.e., 800xc2x0 C.) MgO and MgAl2O4 are formed at about 652xc2x0 F. (i.e., 900xc2x0 C.). On the other hand, the solid solution calcined at less than 1472xc2x0 F. (i.e., 800xc2x0 C.) can be restored in the original structure by hydration.xe2x80x9d (The underlined portions of this passage have been added to convert xc2x0 F. to xc2x0 C. in order to more directly compare the teachings of this reference with other relevant references wherein temperatures are expressed in xc2x0 C., again such comparisons will be made in the next few paragraphs of this patent disclosure)
It might also be noted here that this quotation from the ""118 patent is a precise statement of the temperatures at which certain hydrotalcite decomposition products are described (e.g., spinel, MgAl2O4, formation taking place at 900xc2x0 C. when hydrotalcite is thermally decomposed). This more exact knowledge of the temperatures at which certain aspects of the decomposition of hydrotalcite take place, clarifies many other, more general, statements found in the literature concerning the temperatures at which certain decomposition products are formed (e.g., statements concerned with the temperature at which spinel, MgAl2O4, is formed from a hydrotalcite starting material). That is to say that many, more general, statements concerning the temperatures at which various hydrotalcite thermal decomposition products (e.g., spinel, MgAl2O4) are formed must be carefully interpreted. For example, in U.S. Pat. No. 4,889,615 (xe2x80x9cthe ""615 patentxe2x80x9d) at col. 6, lines 36-43, we find the statement:
xe2x80x9cCalcining the Mg/Al hydrotalcites at temperatures greater than 500xc2x0 C. gives a mixture of MgO and MgAl2O4, a magnesium aluminate spinel, a material which has been reported to reduce FCC regenerator SOx emissions (see U.S. Pat. No. 4,469,589 (Yoo) and U.S. Pat. No. 4,472,267 (Yoo)). The activity of the dehydrated hydrotalcite is, however, significantly different than that observed for the spinel, MgO, or mixtures of both. No evidence of MgAl3812O4 (sic) is observed in the regenerated hydrotalcite indicating that the spinel is not the active component.xe2x80x9d (emphasis added)
Thus, in view of the previous, more precise, descriptions of the temperature of spinel formation (i.e., 900xc2x0 C.) in the ""118 patent, it seems that the more general expression xe2x80x9ctemperatures greater than 500xc2x0 C.xe2x80x9d used in the ""615 patent should not be taken to mean something like 501xc2x0 C., but rather should be taken to mean 900xc2x0 C., a temperature which is indeed xe2x80x9cgreater than 500xc2x0 C.xe2x80x9d It also should be noted that the above-quoted passage recognizes that xe2x80x9cspinel is not the active componentxe2x80x9d of the materials described in the ""615. We note this point here because it is consistent with applicant""s hereinafter described goal of not making spinelxe2x80x94so that applicant""s heat treated, intermediate products can in fact be hydrated (or rehydrated) to form hydrotalcite-like compositions.
A similar general statement concerning spinel formation from a hydrotalcite precursor appears in U.S. Pat. No. 4,458,026. There (at col. 3, lines 54-56) we find the statement:
xe2x80x9cAbove 600xc2x0 C. the resulting metal oxide mixture begins to sinter and lose surface area, pore volume, as well as form a catalytically inactive phase (spinel-MgAl2O4) xe2x80x9d (emphasis added)
Here again, applicant is of the opinion that the general expression xe2x80x9cAbove 600xc2x0 C.xe2x80x9d should not be taken to mean something like 601xc2x0 C., but rather should be taken to mean far enough above 600xc2x0 C. to form spinelxe2x80x94MgAl2O4 that is to say 900xc2x0 C., the temperature at which spinel formation from a hydrotalcite-like compound has been more precisely determined. This quotation also notes that spinel is xe2x80x9ccatalytically inactivexe2x80x9d.
Indeed, one can even find generalized statements about the temperature of spinel formation that are better interpreted to mean lower temperature levels. For example, in U.S. Pat. No. 5,114,898 (at col. 4, lines 43-51) we find the statement:
xe2x80x9cReichle in J. Catal. 101, 352 to 359 (1986) has shown that this heating of hydrotalcite was accompanied by an increase in the surface area from about 120 to about 230 m2/g (N2/BET) and a doubling of pore volume (0.6 to 1.0 cm3/g, Hg intrusion). Further heating to higher temperatures causes lowering of surface area as well as reactivity. At 1000xc2x0 C., the formation of MgO and the spinel phase, MgAl2O4 has been observed.xe2x80x9d (emphasis added)
In this case, applicant thinks that the statement xe2x80x9cAt 1000xc2x0 C. the formation of MgO and spinel phase has been observedxe2x80x9d, is better taken to mean: spinel is observed at 1000xc2x0 C. because spinel (MgAl2O4) forms at 900xc2x0 C.xe2x80x94rather than taken to mean: 1000xc2x0 C. is the temperature of formation of spinel. Indeed, applicant has by his own experimental work confirmed that spinel begins to from in HTL compounds at 900xc2x0 C.
The prior art also has noted that when various anionic clay-forming ingredients such as hydrotalcite-forming ingredients (e.g., magnesium-containing compositions and aluminum-containing compositions) are mixed under certain prescribed conditions (e.g., certain aging times, pH conditions, temperatures, etc.), the resulting slurry or precipitate materials (e.g., hydrotalcite-like materials) will exhibit distinct catalytic properties. Hence, many such production processes are based upon fine tuning of such time, temperature, pH, etc. conditions in order to obtain maximum amounts of a given kind of hydrotalcite-like precipitate product.
The slurry and/or precipitate products of such initial chemical reactions also have been heat treated to obtain various xe2x80x9ccollapsedxe2x80x9d or xe2x80x9cmetastablexe2x80x9d hydrotalcite materials that have specific catalytic properties. Such collapsed materials have, for example, been used as sorbents (and especially SOX sorbents for fluid catalytic and fixed hydrocarbon cracking processes), hydrocarbon cracking catalysts, catalyst binders, anion exchangers, acid residue scavengers and stabilizers for polymers, and even as antacids intended for use in the context of human medicine.
The prior art also has long recognized that other ingredients such as compounds containing Ce, V, Fe and Pt can be added to the original hydrotalcite-forming reaction mixtures so they will appear as a distinct phase of various solid products created by such reactions. Dried forms of such anionic clays (e.g., microspheroidal particles of such hydrotalcite-like compounds used as SOx sorbents in fluid catalytic conversion (FCC) processes) also have been impregnated with solutions of such metals. Moreover, such metals have even been made a integral part of the crystalline structure of hydrotalcite-like materials (see, for example, U.S. Pat. Nos. 5,114,691 and 5,114,898 which teach use of sulfur oxidizing catalysts made of layered double hydroxide (LDH) sorbents, e.g., hydrotalcite-like materials that contain metal ions (e.g., those of vanadium) that replace some or all of the divalent metals (Mg2+) or trivalent metals (Al3+) that form the layers of the LDH).
Hydrotalcite-like compounds that are used as catalysts also have been both heat treated and associated with various catalyst binder or matrix materials. For example, U.S. Pat. No. 4,866,019 (the ""019 patent) discloses that hydrotalcite can be heat treated and used in association with various binder materials. U.S. Pat. No. 5,153,156 teaches a method for making magnesium/aluminum synthetic anionic clay catalysts by (1) spray drying a slurry of a magnesium aluminum synthetic clay, (2) making a plasticized mixture of the spray dried clay with diatomaceous earth and (3) forming, drying and calcining the resulting plasticized mixture.
The prior art also has long recognized that anionic clay materials can be used to catalyze certain specific chemical reactions. For example, U.S. Pat. No. 4,458,026 teaches use of certain heat treated anionic clay materials as catalysts for converting acetone to mesityl oxide and isophorone. The anionic clays are given this catalytic activity by heating them to temperatures ranging from about 300 to 600xc2x0 C.
U.S. Pat. No. 4,952,382 teaches a hydrocarbon conversion process that employs a catalyst composition containing an anionic clay wherein the anionic clay serves as a sulfur oxides binding material.
U.S. Pat. No. 4,970,191 teaches use of polymorphic magnesium-aluminum oxide compositions as catalysts in various base catalyzed reactions such as alcohol condensation, isomerization of olefins, etc.
U.S. Pat. No. 4,889,615 discloses a vanadium trap catalyst additive comprising a dehydrated magnesium-aluminum hydrotalcite.
U.S. Pat. No. 5,358,701 teaches the use of layered double hydroxide (LDH) sorbents such as hydrotalcite-like materials as SO2 sorption agents. This reference postulates that the sulfur-containing gas absorbs into the hydrotalcite structure as SO32xe2x88x92 anions by replacing the gallery CO32xe2x88x92 anions. The absorbed sulfur is thereafter driven off by calcination at elevated temperatures (500xc2x0 C. ). The LDH sorbents are regenerated by hydrolyzing the calcined product, particularly in the presence of CO2 or CO32xe2x88x92.
U.S. Pat. No. 5,114,691 teaches removing sulfur oxide from gas streams using heated layered double hydroxide (LDH) sorbents having metal-containing: oxoanions incorporated into the galleries of the LDH structures.
U.S. Pat. No. 4,465,779 teaches catalytic cracking composition comprising a solid, cracking catalyst and a diluent containing a magnesium compound in combination with a heat-stable metal compound.
U.S. Pat. No. 5,426,083 teaches catalytic use of a collapsed composition of microcrystallites comprised of divalent metal ions, trivalent ions, vanadium, tungsten or molybdenum.
U.S. Pat. No. 5,399,329 teaches making hydrotalcite-like materials by preparing a mixture of magnesium (divalent cation) to aluminum (trivalent cation) in a molar ratio between 1:1 and 10:1, and in a mono carboxylic anion to aluminum (trivalent cation) molar ratio between 0.1:1 to 1.2:1. The process involves reacting a mixture comprising magnesium and aluminum cations and mono carboxylic anions in an aqueous slurry having a temperature of at least 40xc2x0 C. and a pH of at least 7. Generally speaking, a given synthesis of a HTL compound by any of the methods taught in these patents was considered a success when the product of its chemical synthesis reaction (slurries typically were heated and/or pressured to form a final dry product or precipitate) produces a given HTL compound having an x-ray diffraction pattern which reasonably resembles that of a given card in the files of the International Center for Diffraction Data (xe2x80x9cICDDxe2x80x9d).
In summarizing the prior art, it might be said that most methods that have been employed to produce anionic clay compounds, and especially hydrotalcite-like, anionic clay compounds, usually involve precipitation or slurry drying of a hydrotalcite-like product, washing and, optionally, heat treatment of the resulting dried slurry, or precipitated, composition. Once made, these HTL compounds, or their thermal decomposition products, have been employed as catalysts (e.g., as vanadium passivators, SOx additives, aldol condensation catalysts, water softening agents, and even medicines).
Applicant""s contribution to this art has been to discover certain hereinafter described methods, whereby HTL compounds can be produced from compounds that do not exhibit HTL structures (e.g., as determined by their XRD patterns), but which do exhibit HTL structures upon being activated by the processes of this patent disclosure. Applicant also has discovered certain novel methods whereby anionic clays in general and hydrotalcite-like compounds in particular can be given certain attributes (increased hardness, density, etc.) that make such compounds better suited for uses where these attributes are desirable, e.g., as sorbents for various chemical speciesxe2x80x94but especially SOx sorbentsxe2x80x94and especially those SOx sorbents (and binder materials) used in FCC units, as hydrocarbon catalysts, as water softening agents, etc.
Again, those compounds generally described as xe2x80x9canionic claysxe2x80x9d in the literature, and especially hydrotalcite, and HTL anionic clay compounds, will be collectively referred to as xe2x80x9cHTL compoundsxe2x80x9d for the purposes of this patent disclosure. More specifically this invention involves formation of hydrotalcite-like compounds by certain novel production methods and the use, of certain formed shapes (microspheroidal particles, extrudates, pellets) containing those hydrotalcite-like compounds produced by applicant""s processing techniques. For example, these formed shapes (e.g., microspheroidal particles, pellets, extrudates, etc.) for certain specific catalytic uses (e.g., FCC operations, SOx sorption, water softener regeneration agents, etc.). Hence, the HTL compounds of this patent disclosure may constitute part of (or even all of) a given catalyst particle, pellet, extrudate, etc. By way of example the HTL compounds of this patent disclosure may be associated with various binder or matrix forming materials known to the catalyst making art. Indeed, the HTL compounds of this patent disclosure may be used as catalysts per se (e.g., as hydrocarbon cracking catalysts), as SOx binding agents, or as catalyst binder materials for other catalyst materials. Hence, for the purposes of this patent disclosure the term xe2x80x9ccatalystxe2x80x9d should be taken to mean not only those HTL compounds that have catalytic or SOx binding activity in their own right, but also those HTL compounds that are used as binders, matrices and/or carriers for other catalytically active compounds (e.g., binders for metallic, SOx oxidation catalysts such as compounds containing platinum, cerium and vanadium). These applications are all related to the fact that the HTL compounds produced by applicant""s methods can, among other ways, be characterized by their resistance to mechanical stresses and, hence, by their ability to function in the severe environments associated with many chemical reactions.
Applicant""s overall invention is primarily based upon a two step xe2x80x9cactivationxe2x80x9d procedure that is generally comprised of heat treating and then hydrating certain hereinafter described hydrotalcite-producing, precursor compounds. This two step process may, in some cases, be augmented by an additional, but purely optional, heat treatment step (which may be referred to as Step 3 of applicant""s process). These heat treated compounds may be thought of xe2x80x9ccollapsedxe2x80x9d or xe2x80x9cmetastable,xe2x80x9d HTL compound-forming materials.
Applicant""s invention has two general embodiments. The first embodiment is a method for producing HTL compounds (e.g., anionic clay compounds, hydrotalcite per se, and various hydrotalcite-like compounds) from compounds that do not possess the structural characteristics of HTL compounds. The manner by which this first embodiment of applicant""s invention differs from prior art methods for making similar HTL compounds is that applicant""s initial HTL synthesis is carried out using those ingredients and those reaction conditions which are such that they do not directly produce compounds having a HTL structure, but rather produce compounds that exhibit a HTL structure only after experiencing applicant""s hereinafter described activation process. Hence, in the first embodiment of this invention, an actual XRD determination that the product of applicant""s initial slurry or precipitation synthesis reaction does not produce a compound having an XRD pattern that reasonably resembles that of a compound having the proper ingredient atoms (e.g., those of magnesium, aluminum, oxygen and hydrogen in the case of HTL compounds) on file with the ICDD could be an optional step in applicant""s overall process.
It also should be specially noted, however, that applicant""s synthesis products may well include xe2x80x9camorphousxe2x80x9d (non-crystalline) materials as well as non-HTL, crystalline phasesxe2x80x94and combinations thereof. Indeed, the term xe2x80x9camorphousxe2x80x9d as used herein could include (1) crystalline phases which have crystallite sizes below the detection limits of conventional x-ray diffraction techniques, (2) crystalline phases which have some significant degree of ordering, but which lack a crystalline diffraction pattern due to dehydration or dehydroxilization (such as in layered aluminosilicates) , and (3) true amorphous materials which may exhibit short range order, but no long- range order, such as, for example, silica and borate glasses.
Whatever their physical form (crystalline or amorphous), these precursor, synthesis reaction products may be subjected to some form of xe2x80x9clow temperaturexe2x80x9d (i.e., xe2x80x9clow temperaturexe2x80x9d may be taken to mean less than about 250xc2x0 C., for the purposes of this patent disclosure) drying process before they undergo the heat treatment aspect of applicant""s activation process. Such a low temperature drying process also may include the physical formation of those powders, pellets, beads, extrudates, microspheroidal spheres or granule forms of these reaction product materials that may be required (or desired) for use of these materials as catalysts, sorbents, ion exchange agents, etc. This drying step should, however, be considered xe2x80x9coptionalxe2x80x9d because the most fundamental version of the first embodiment of applicant""s invention could go directly to its heat treatment step.
This heat treatment step involves heating applicant""s synthesis reaction products to a xe2x80x9cmedium temperaturexe2x80x9d (i.e., a temperature in the range of about 300xc2x0 C. to about 850xc2x0 C.). This heat treatment may be carried out for widely varying periods of time (e.g., from for about 0.1 to about 24.0 hours. This 300xc2x0 C.-850xc2x0 C. heat treatment step may generally be referred to as Step 1 of applicant""s overall xe2x80x9cactivationxe2x80x9d process. It is more preferred, however, that Step 1 be conducted at a temperature on the low-end of this 300xc2x0 C.-850xc2x0 C. range. This treatment may be carried; out at some preferred temperature (e.g., 450xc2x0 C.) or at different temperatures in this 300xc2x0 C. to 850xc2x0 C. range. Step 1, medium temperature, heat treatments in the range of about 400xc2x0 C. to about 500xc2x0 C. are, however, highly preferred. Temperatures at the upper end of applicant""s 300xc2x0-850xc2x0 C. range, such as temperatures ranging from about 700xc2x0-850xc2x0 C., are less preferred since various less desirable phases (hereinafter more fully described) may result from heating applicant""s precursor, synthesis reaction products to such levels. The formation of these less desirable phases may diminish the precursor material""s potential to form maximum amounts of the HTL-containing phases that are the object of applicant""s processes.
These higher temperatures also are less preferred because they come dangerously close to the 900xc2x0 C. temperature at which a particularly undesirable materialxe2x80x94namely, spinel (MgAl2O4) begins to form. Again, applicant regards spinel formation as xe2x80x9canathemaxe2x80x9d to this process because spinel can not be rehydrated. This is not to say however that any other material, e.g., MgO, that be present in such a system at temperatures at or above 900xc2x0 C., can not be employed for applicant""s purposes. For example, if applicant""s hydrotalcite-like starting material is converted into spinel (MgAl2O4) it becomes useless for applicant""s purposes; if, however, applicant""s starting material is converted into MgO, it still may be useful (e.g., as an SOx sorbent agent).
In any event, temperatures of 900xc2x0 C. or higher can be regarded as xe2x80x9chigh temperaturesxe2x80x9d for the purpose of this patent disclosure and they are to be avoided as far-as possible. This admonition also is consistent with the teachings and spirit of the literature. That is to say that nowhere does the literature even remotely suggests that spinel can be reversibly hydrated into any other phase at ambient temperatures. By way of sharp contrast with this, the literature teaches that HTL compounds such as applicant""s, very decidedly possess the characteristic of rehydratability.
The literature also teaches that the basic structural building block of HTL, the brucite structure, Mg(OH)2, also possess this xe2x80x9crehydratabilityxe2x80x9d characteristic. It is also known that, if the crystal size of such materials grows significantly (as it does with increasingly higher thermal treatment temperatures), then such xe2x80x9creversibilityxe2x80x9d is eventually lost. Consequently, the brucite layer no longer forms upon rehydration. This is the same situation applicant expected, and in fact observed, for various HTL compounds made by the teachings of this patent disclosure. Indeed, applicant found that as temperature increases beyond certain levels, an increase in a MgO-like material""s crystallite size, as well as alumina and magnesium aluminate (spinel) formation, eventually do take place. Consequently, for maximum SOx activity of applicant""s HTL compounds, it is preferred that all the MgO in a given system remain with the HTL phase as opposed to reacting with other phases and thereby rendering the MgO xe2x80x9cinactivexe2x80x9d e.g., inactive as a SOx xe2x80x9cpickup agent.xe2x80x9d Again, this is best achieved by not using temperatures above about 850xc2x0 C.
In any case, the heat treated product of Step 1 of applicant""s xe2x80x9cactivationxe2x80x9d process is then subjected to a hydration step. This hydration step might be termed Step 2 of applicant""s activation procedure. It generally entails mixing the heat treated product of Step 1 with a quantity of moisture which is such that heat is evolved from the heat treated precursor material/liquid (e.g., water) mixture. The method or manner of hydration to effect applicant""s Step 2 will include, but not limited to such methods as spraying, impregnating and blunging.
In any case, the heat release produced by this hydration is indicative of the heat of formation of a HTL compound. Additionally, this heat release signifies the occurrence of the chemical reaction which is presumed to be the cause of the greatly improved physical properties of HTL compounds prepared by the methods of this patent disclosure. It also should be noted here that in order to maximize the amount of HTL compound produced by this hydration step, the amount of water added should be substantial in quantity (on the order of 30-50 weight percent of the dry, precursor material). Such amounts of water are required in order to fully form HTL phases although less water will still result in a material that exhibits a HTL phase; such a phase will not, however:, be xe2x80x9cpure,xe2x80x9d i.e., other collapsed HTL phases will be present (i.e., a MgO-like phase and/or a MgAl solid solution phase).
Again, depending on the hydration method to be employed, the previously noted xe2x80x9clow temperature,xe2x80x9d optional drying step also may be employed in order to render a material having a desired amount of physical water. And, once again, this low temperature drying should not exceed about 250xc2x0 C. because applicant has found that temperatures in excess of this may result in a premature release of various interlayer ions, water, crystalline water, or certain carbonates. In any case, the HTL compound product produced by applicant""s hydration step will possess a crystalline structure which exhibits an x-ray diffraction pattern that may, and probably will, reasonably resemble a ICDD xe2x80x9ccardxe2x80x9d for some HTL compound that has a similar crystalline structure.
In some cases this hydrated product may again be xe2x80x9ccollapsedxe2x80x9d by a second heat treatment step which might be called Step 3 of applicant""s process (e.g., Step 3 heat treatments at temperatures ranging from about 300xc2x0 C. to 850xc2x0 C. and preferably at 400xc2x0 C. to 500xc2x0 C.) in order to remove its interstitial water so that the resulting material is better suited to certain uses such as a SOx sorbent in a FCC unit. Compounds created by this third step may be used for any of the purposes for which the HTL compounds created by applicant""s Step 1 and Step 2 materials may be used.
From a broad conceptual point of view, the most fundamental version of the first embodiment of applicant""s invention might be thought of as being based upon: (1) a xe2x80x9cdelayxe2x80x9d in the production of a hydrotalcite-like compound end product relative to the point at which analogous hydrotalcite-like compounds have been made by prior art production methods, (2) heat treatment (single stage or multiple stage) of these xe2x80x9cnot yetxe2x80x9d (e.g., with this xe2x80x9cnot yetxe2x80x9d quality or state being determined by XRD methods) hydrotalcite-like materials and (3) hydration of the these heat treated materials to form hydrotalcite-like compounds. Stated another way, it might be said that the goal of applicant""s initial synthesis or chemical reaction step is to not make as much of a subject, end product, HTL compound as possible (e.g., not to make as much hydrotalcite as possible), but rather to make as little of the desired end product compound, (e.g., to make as little hydrotalcite) as possible.
In any event, applicant""s first general process may generally employ any combination of those HTL compound creating starting ingredients (e.g., magnesium-containing compounds having less reactive anions and aluminum-containing compounds having less reactive anions) and any of those reaction conditions (e.g., short reaction aging times, neutral pH levels, and ambient temperatures reaction conditions) that may serve toxe2x80x94and, indeed, strive toxe2x80x94produce a resulting slurry or precipitate material that does not exhibit the crystalline structure of the HTL compound that ultimately will be exhibited by applicant""s end product hydrotalcite-like compound. In fact, the precursor compounds obtained by the initial chemical reaction step of applicant""s first process may well be entirely amorphous materials having no HTL structure whatsoever.
In the second embodiment of applicant""s invention, however, a hydrotalcite-like compound is purposely used as the starting material, or as a precursor compound. That is to say that a hydrotalcite-like starting material can be purchased commerciallyxe2x80x94or it can be synthesized by use of any of the many methods known to this art and then be employed according to the teachings of this patent disclosure. In either case, however, applicant""s process calls for heat treatment of the hydrotalcite-like compound (however obtained) to form a xe2x80x9ccollapsedxe2x80x9d or xe2x80x9cmetastablexe2x80x9d material. This heat treatment also may be: thought of as Step 1 of this second embodiment of applicant""s invention. The collapsed or metastable material of this second embodiment is then hydrated to again form a hydrotalcite-like compound. This hydration may be thought of as Step 2 of this second embodiment of applicant""s invention. Applicant has found that this xe2x80x9croundaboutxe2x80x9d method of producing a hydrotalcite-like compound (from a hydrotalcite-like compound) is well worth the extra effort because the resulting hydrotalcite-like compound will be harder and/or more dense than the original hydrotalcite-like compound from which the resulting HTL compound was made.
Stated another way, the starting ingredient in the second embodiment of applicant""s invention already will be a rehydratable hydrotalcite-like compound. This may be evidenced, for example, by the fact that it already generally displays XRD peaks that resemble those of a known HTL compound having the same ingredients (e.g., Mg and Al). In any case, this hydrotalcite-like compound starting material is then heat treated to convert it into a xe2x80x9ccollapsedxe2x80x9d or xe2x80x9cmetastablexe2x80x9d compound such as those described in the Miyata reference, or in the ""118 patent. The Step 2, heat treatment of the second embodiment of this invention can be conducted at a single preferred temperature (e.g., 450xc2x0 C.) or at two or more distinct temperatures in the general temperature range of 300xc2x0 C. to 850xc2x0 C. , e.g., at a first, lower temperature, (e.g., at 300xc2x0 C.) followed by a second temperature heat treatment (e.g., at 400xc2x0 C. to 500xc2x0 C.). Here again, however, temperatures greater than about 850xc2x0 C. are to be avoided in this second embodiment of applicant""s process for the same reasons they were to be avoided in the first embodiment. For example, if the original synthesis compound were hydrotalcite, and it experienced a 900xc2x0 C. heat treatment temperature for any significant period of time in the second embodiment of applicant""s invention, it too would in fact be converted it into spinel (MgAl2O4) and, thus, would be rendered useless for the purposes of practicing this invention. Here again, any hydrotalcite converted to MgO by such high temperatures would, however, still be potentially useful in carrying out functions for applicant""s end product materials.
In any case, after the hydrotalcite-like compound of this second embodiment is heat treated to an extent that it takes on a xe2x80x9ccollapsedxe2x80x9d or xe2x80x9cmetastablexe2x80x9d form, it can then hydrated (e.g., in a water system at 20-100xc2x0 C. for at least 0.1 hours) in the same manner employed in the first embodiment of this invention to again form a similar hydrotalcite-like compound. Again, this xe2x80x9chydrotalcite-like compoundxe2x80x94to hydrotalcite-like compoundxe2x80x9d production process is not a useless, redundant or roundabout journey because the hydrotalcite-like compounds resulting from this second embodiment of applicant""s invention will, in fact, have certain improved physical and/or chemical properties (e.g., greater density, attrition resistance, catalytic activity, etc.) relative to those comparable properties possessed by the original hydrotalcite-like compound from which the resulting or end product hydrotalcite-like compound was derived. And as in the case of the first embodiment of this invention, the resulting HTL compound of this second embodiment can be once again heat treated (this may be thought of as Step 3 of this second embodiment) at temperatures ranging from about 300xc2x0 C. to 850xc2x0 C. in order to obtain a yet harder material whose loss of water due to this second heat treatment may render the resulting material better suited to certain uses (e.g., as a SOx absorbent in a FCC unit). That is to say that Step 3 can be employed to give the resulting material (here again, a xe2x80x9ccollapsedxe2x80x9d or xe2x80x9cmetastablexe2x80x9d HTL compound-forming material) improved physical properties relative to those HTL compounds that are not subjected to this additional heat treatment process.
The anionic compounds that can be produced by the hereindescribed processes will most preferably have a chemical structure:
[Mm2+Nn3+(OH)2m+2n]An/aaxe2x88x92.bH2O
wherein M2+ and N3+ are cations, m and n are selected such that the ratio of m/n is about 1 to about 10, a will have a value of 1, 2 or 3, A is an anion with charge of xe2x88x921, xe2x88x922 or xe2x88x923, and b will range between 0 and 10, are highly preferred. The most preferred elements for xe2x80x9cMxe2x80x9d in the above structure will be Mg, Ca, Zn, Mn, Co, Ni, Sr. Ba, Fe and Cu. The most preferred element for xe2x80x9cNxe2x80x9d will be Al, Mn, Fe, Co, Ni, Cr, Ga, B, La and Ce. The most preferred elements for xe2x80x9cAxe2x80x9d with charge axe2x88x92 will be CO32xe2x88x92, NO3xe2x88x92, SO42xe2x88x92, Clxe2x88x92 and OHxe2x88x92, Crxe2x88x92, Ixe2x88x92, SO42xe2x88x92, SiO32xe2x88x92, HPO32xe2x88x92, MnO42xe2x88x92, HGaO32xe2x88x92, HVO42xe2x88x92. ClO4xe2x88x92 and BO32xe2x88x92 and mixtures thereof.
Applicant generally has found that HTL compounds made by either of the two general embodiments of this invention are usually at least about 10% harder and/or 10% more dense than comparable HTL compounds made from the same ingredients by prior art production methods. These physical attribute(s), e.g., of hardness and/or greater density, makes those catalysts, sorbents, catalyst binders and ion exchange agents (e.g., water softener agents) made from applicant""s hydrotalcite-like compounds more attrition resistantxe2x80x94and hence longer lastingxe2x80x94especially in a fluid catalytic converter (xe2x80x9cFCCxe2x80x9d) environment. Applicant""s resulting compounds also have an improved ability to be regenerated (e.g., with respect to their ability to continue to serve as SOx sorbents, hydrocarbon cracking (or hydrocarbon forming) catalysts, ion exchange agents, etc.) after having experienced temperatures which would permanently deactivate analogous anionic clays (such as analogous hydrotalcite-like compounds) made by prior art manufacturing methods. Indeed, these improved physical attributes can be thought of as even further helping to define applicant""s materials and distinguish them from analogus HTL compounds made by prior art methods. That is to say that, if applicant""s xe2x80x9cactivationxe2x80x9d procedures (using Steps 1 and 2 or using Steps 1, 2 and 3) produce, say, a hydrotalcite-like compound exhibiting greater hardness and/or greater density than a comparable hydrotalcite-like compound made by other methods, then these qualities may help to distinguish applicant""s xe2x80x9chydrotalcite-like compoundsxe2x80x9d from those made by prior art methods.
Because the HTL compounds of this patent disclosure are harder than HTL compounds made by prior art processes, they present a method whereby the useful life of a catalyst or sorbent system (such as those employed in FCC units or fixed bed units) can be extended. This extension of a catalyst""s (or sorbent""s) useful life will take place when the HTL compounds of this patent disclosure are used in their own right, e.g., as hydrocarbon cracking or forming catalysts, SOx sorbents, etc., or when these HTL compounds are used as binders, matrices, supports, or carriers for other catalytically active materials (e.g., when they are used as binders for SO2xe2x86x92SO3 oxidant metals).
Thus, using SOx sorption in a FCC unit used to refine petroleum as an example, the method of extending the useful life of an SOx sorbent (or catalyst) may be expressed in patent claim language in the following manner:
A method for extending the useful life of a SOx sorbent system used in a FCC unit being employed to refine a petroleum feedstock, said method comprising: employing a HTL compound made by use of a process of this patent disclosure as a SOx sorbent system in the FCC unit and wherein the HTL compound is in the form of a microspheroidal particle species whose primary function is sorbing SOx produced by refining a sulfur-containing petroleum.
Such a HTL compound-containing particle species may further comprise a binder agent selected group consisting of magnesium aluminate, hydrous magnesium silicate, magnesium calcium silicate, calcium silicate, alumina, calcium oxide and calcium aluminate.
Expressed in patent claim language, such a method for extending the useful life of a SOx additive system comprised of a SO2xe2x86x92SO3 oxidation catalyst and a SO3 sorbent may comprise:
(1) employing the SOx additive system in the form of at least two physically distinct particle species wherein a first particle species contains the SO2xe2x86x92SO3 oxidation catalyst component and carries out a primary function of oxidizing sulfur dioxide to sulfur trioxide and the second particle species is physically separate and distinct from the first particle species and carries out a primary function of sorbing the SO3 produced by the SO2xe2x86x92SO3 oxidation catalyst;
(2) employing the SO2xe2x86x92SO3 oxidation catalyst in the form of a particle species that comprises: (a) a sulfur SO2xe2x86x92SO3 oxidation catalyst comprised of a metal selected from the group consisting of cerium, vanadium, platinum, palladium, rhodium, molybdenum, tungsten, copper, chromium, nickel, iridium, manganese, cobalt, iron, ytterbium, and uranium; and (b) a binder made from a material selected from the group of metal-containing compounds consisting of hydrotalcite-like compounds, calcium aluminate, aluminum silicate, aluminum titanate, zinc titanate, aluminum zirconate, magnesium aluminate, alumina (Al2O3), aluminum hydroxide, an aluminum-containing metal oxide compound (other than alumina (Al2O3)), clay, zirconia, titania, silica, clay and clay/phosphate material; and
(3) using the SO3 absorbent component in the form of a second particle that comprises a hydrotalcite-like compound made by use of an xe2x80x9cactivation processxe2x80x9d of this patent disclosure.
This activation process may involve use of Step 1 and Step 2 (or Steps 1, 2 and 3) upon a non-hydrotalcite-like starting material or a hydrotalcite-like starting material. Any of the HTL compounds may be used in FCC systems wherein the SOx sorbent particle species comprises from about 10 to about 90 weight percent of the overall SOx additive system (i.e., the SOx sorbent particle species and the SO2xe2x86x92SO3 oxidant particle species). Such an overall, SOx additive system will, in turn, normally comprise from about 0.5 to about 10.0 weight percent of a bulk hydrocarbon cracking catalyst (e.g., zeolite) SOx additive system.
Next, it should be understood that the HTL compounds made by any of these methods may be used in any way that the prior art has used hydrotalcite-like compounds made by any prior art method (e.g., they may be used as sorbents and especially SOx sorbents, hydrocarbon cracking catalysts, e.g., for use in fixed bed or fluid bed systems, catalyst carrier or binder materials, anion exchangers (e.g., water softener agents, etc.) acid residue scavengers, stabilizers for polymers, medicines, etc.). Applicant""s HTL compounds are, however, particularly useful where the attributes of physical hardness, toughness, or greater density are especially desired (e.g., when they are used in FCC units as SOx sorbents, catalysts and catalyst binders or carriers).